Following this, NM techniques are applied to monitor microcracking generated by unstable archeological caverns that were excavated in natural chalk. Although signals can be detected in unfavorable signal-to-noise ratio conditions by a single array at slant-distances beyond 102 m, reliable locations can only be obtained when several mini-arrays are deployed in the vicinity of caverns suspected to be unstable. Epicentral locations of microcracking events tend to cluster near free boundaries and in zones of high tensile stress, as predicted by numerical models computed for these caverns. These results confirm the operative capacities of low-cost NM techniques in locating and analyzing pre-failure microcracking processes occurring within weak natural media. Complex source processes, which occur at distances that exceed the detection range of standard acoustic emission and ultrasonic monitoring, can be fully evaluated using portable equipment that can be deployed within minutes with no prior infrastructure.